CANBERRA, AUSTRALIA - MAY 20: Shadow Treasurer Chris Bowen gives his budget reply address at the National Press Club on May 20, 2015 in Canberra, Australia. The Labor Party assert the current Superannuation tax concessions are unaffordable and need to be changed, following last weeks 2015 Federal budget announcement. (Photo by Stefan Postles/Getty Images)

The federal opposition has defended its proposed changes to negative gearing rules, describing it as "big, bold policy" reform that puts first homebuyers on a more level playing field.

On Saturday, Labor announced key tax policy measures that included the restriction of negative gearing to newly constructed homes and a reduction in the capital gains tax discount from 50 to 25 percent.

Under a Shorten Labor Government, from July 2017, negative gearing will only be available on newly-constructed homes and there would be no change for existing negatively geared property.

On Sunday, Shadow Treasurer Chris Bowen rejected claims the changes would lead to a bubble for existing homes.

"People will obviously continue to invest in existing homes after 1 July 2017, they will be able to continue to invest in those for rental purposes but if they want to claim their losses on their property against their salary, then they will need to invest in new houses," Bowen told ABC television.

"I think that will lead to an increase in supply in new houses and apartments."

He denied that the changes would make it more risky to invest in new homes.

"That's not in any sense any more risky than buying an existing property," he said.

"There's an element of risk to any investment. So some people think property never goes down, sometimes it does, but that applies to existing properties as well as new."

The comments come after Labor announced on Saturday what it called the biggest tax reform in a decade.

In addition to negative gearing changes, Labor's plans also include alterations to capital gains laws.

The ALP's reforms would see capital gains tax concessions cut from 50 per cent to 25 percent in July 2017, while the opposition is not proposing to change the rules on existing assets and personal superannuation related to capital gains tax.

The family home would be 100 percent capital gains tax-free under the reforms.

Opposition leader Bill Shorten said the changes would save $32.1 billion and help put fairness back into the housing market.